Power Auto-transformer Mechanical Faults Diagnosis ‎Using Finite Element based FRA

Frequency response analysis (FRA) is a sensitive ‎method established for testing the mechanical integrity of ‎transformers. However, interpretation of FRA signature still ‎needs expert opinions and there is no FRA interpretation code ‎generally accepted. Various mechanical faults with different ‎extents on power transformers are required to aid FRA ‎interpretation. To address this challenge, in this paper a high ‎definition 3D FEM model of a three-phase, three-winding, 125-‎MVA power auto-transformer was constructed using finite ‎element method and verified by experimental FRA ‎measurements. Various radial deformations and axial ‎displacements were formed using FEM model and the extracted ‎parameters of the winding detailed model were used to obtain ‎power transformer frequency responses. The commonly used ‎appropriate statistical indices in FRA diagnosis were utilized for ‎interpreting FRA results. The study showed that the frequency ‎range between 1-100 kHz is mainly affected by the mechanical ‎faults and the 1st resonance of the double-peak feature of the ‎auto-transformer FRA remains unchanged during winding ‎radial deformation and axial displacement.‎